For a number of years during cotton harvest in California's San Joaquin Valley, a decrease in cotton plant height was noted in the rows adjacent to the traffic path of the tractor. Studies which measured soil compaction and cotton yields for several tractor configurations were conducted over two growing seasons. The first year's study consisted of sandy and clay test plots with four tractor configurations. The highest yield was with a conventional wheel tractor with dual rear tires and front wheel drive. The plot yielded 27% more cotton in the sandy field and 14% more in the clay field over the least producing tractor plot, which was the belted track tractor. In the second year's study, the highest yield was also with a conventional wheel tractor with dual rear tires and front wheel drive. The plot produced 5% more cotton over the least producing tractor plot, also a belted track tractor. Cotton yields correlated with the soil compaction (cone penetrometer) measurements.